Container for molten metal



Nov. 20, 193.4. H. HILL CONTAINER FOR MOLTEN METAL Filed June 19, 1934 2 Sheets-Sheet 1 Fig.3.

l I 28 I, I 4? I l //v vs/vro'k hw ltdl mpw A TTORNE rs Patented Nov. 20, 1934 CONTAINER FOR MOLTEN METAL Harry Hill, Kent, England, assignor to Callenders Cable and Construction Company Limited,

London, England, a British company Application June 19, 1934, Serial No. 731,278 In Great Britain July 14,1933

6 Claims.

In many cases the vessels which contain molten metal (either vessels in which the melting occurs or vessels which serve for the storage of molten metal) leave the surface of the metal exposed to the atmosphere. Under these conditions gas, usually oxygen, can be and'is readily absorbed by the molten metal. This results in wastage of the metal and in the disturbance of the proportions of alloys by preferential combination with the-gas and also involves the risk of including oxides or other compounds in the molten metal when it is drawn off.

Bythe present invention the surface of the molten metal, in cases such as above indicated, is covered almost completely by a floating body which prevents or greatly reduces the disadvantageous effect mentioned; The float will be a body of solid material, which is structurally stable at the temperature of the molten metal, will not hold an appreciable'quantity of occluded gas and is not soluble in or liable to combine, with the molten metal to an appreciable or disadvantageous extent. Usually the float will be made of metal and will be in the form of a plate or shallow tray or box which follows the shape of the vessel allowing only suflicient clearance to ensure free movement as the level of the molten metal rises and falls. It will be clear that it is important'that the vessel should have vertical or approximately vertical sides. It will be advantageous to provide on the under surface of the floatone or more continuous downwardly extending flanges. If a float with a flat lower surface without flanges is provided, it is possible for gas from the surrounding atmosphere to combine with the metal at the small exposed surface between the float and the wall of the vessel and by this combinationto pass to the metal under the float. By providing a flange along the edge of the float extending downward an appropriate distance, the possibility of this action is removed since any compound which is formed floats on the top of the metal in the space between the flange and the wall of the vessel and either will not be produced in sufficient quantity to extend below the flange or can readily be removed at intervals before accumulating to a sufficient depth to pass under the flange. An inner flange may be provided if there is risk of the outer flange being passed. A similar flange will also be provided round any aperture which it may be necessary to provide in the float.

The explanation of the use of the invention and the advantageous results obtained in con nection with lead will now be given as an illustration of the invention and its possibilities.

When lead or lead alloys are melted in the open type of melting pot appreciable surface oxidation occurs; In the case of high grade lead thick layers of oxide or dross are formed, since the underlying'lead can obtain its oxygen from the layers of oxide above it. In the case of the lead alloys containing tin, antimony, etc. in common use the added elements which are required in the finished product are oxidized out preferentially and hence lost.

The accompanying drawings illustrate the application of the present invention to an open type of melting pot for lead or lead alloys. In these drawings, which show,'by way of example, one form of construction of float,

Figure 1 is a plan of the float in place in its melting pot,

Figure 2 is a vertical cross-section of the pot and its float taken on the line II-II in Figure 1,

Figure 3 is a vertical cross-section of the float taken on the line III III in Figure l and Figure 4 is a vertical cross-section of the float taken on the line IV-IV in Figure 1.

Referring now to the drawings it will be seen that the upper part of the wall of the lead melting pot 1 is cylindrical. The float 2 is of corresponding shape, having an overall diameter slightly less thanthe internal diameter of the pot 1, thus providing small clearance 3 between it and the pot. This allows it always to float on the surface 4 of the molten metal 5 and rise or fall in the pot as the level of the molten metal is varied and yet stillseal'practicallythe whole surface of the metal from the atmosphere. In order to reduce to a minimum the exposure of the surface of the metal when the ingots are charged into the melting pot, the float is provided with a charging aperture 6 of a shape and size suited to the ingots to be used. Normally this aperture is closed by two trap doors '1.

The mild steel body of the float is of welded construction. It comprises a grid-like frame, consisting of the cylindrical wall 8 of the float and of vertical ribs 9, 10, 11. This frame is covered in, except for the charging aperture 6, on both sides by cover plates. The two ribs 9 extend right across the float. These and the two ribs 10 are equal in depth to the cylindrical wall 8 but the ribs ll running from the wall 8 to the ribs 9 are of less depth to avoid having to divide the under cover plate 12 into more than four parts.

This cover plate is located above the lower edges 11o of the cylindrical wall 8 and of the Walls of the charging aperture 6 and is welded to the adjacent surfaces of these walls and to the lower edges of the ribs 11. By this it is provided that the lower parts of the wall 8 and ribs 9 and 10 form flanges around the edges of the float and of the charging aperture which extend downwardly into the molten metal. The pockets 13 formed between the ribs and the cylindrical wall are packed with lagging material (not shown). On the upper face of the frame is a detachable cover comprising a disc of asbestos mill-board 14 and a mild steel plate 15, both being apertured to correspond with the charging aperture 6 in the body of the float.

The trap doors 7 are pivotally supported in bearings 16 welded to the ribs 9. These doors embody the same principles of construction as does the float itself, that is to say each is built up from walls and from upper and lower cover plates, 17 and 18, respectively, to form a cell 19 which is packed with lagging material (not shown). The side walls 20 of the doors are vertical to permit the doors to open inwardly and normally to close the aperture except for a small clearance 21 between them and the vertical side walls of the charging aperture 6. The lower edges of the walls are arranged to lie always below the surface of the molten metal. The end wall which lies nearer to the pivot pin 23 and is designated by the numeral 22 is vertical from its upper edge to the level of the pivot pin axis; below this point the wall is arcuate in section and forms a quarter of a cylinder of which the axis is coincident with that of the pivot pin. This construction permits the small clearance 24 between this end wall of the door and the adjacent end wall of the aperture to be maintained constant as the door is opened in a downward direction and ensures that none of the lower edges of the door walls is withdrawn clear of the molten metal. Access of air or scale to the surface of the metal underneath the door is thus avoided. The other end wall 25 of the door is arranged to make a contact with the corresponding wall of the other door over a substantial area when the doors are in their normal position. Both trap doors are furnished with a handle 26 and to facilitate the introduction of the ingots both have sloping upper surfaces and the smaller has a roller 27. Normally the charging aperture 6 is maintained closed by the upward thrust exerted on the doors '7 by the molten metal but under the weight of an ingot the doors are opened, closing again automatically as the ingot slides off into the molten metal. Consequently, the action of these doors is mainly automatic.

Vent holes 28 and vent pipes 29 are provided to allow the escape of gases which may be cc cluded in the unmelted ingots and which are liberated as the metal becomes molten. By this means the possibility is avoided of the float being raised by the pressure exerted by gas trapped in the cavities 30 on the under side of the float and of the downwardly extending flanges being rendered less effective. Lifting eyes 31 are provided to enable the float to be lifted clear of the pot to permit periodic removal of the dross.

Tests show that with the use of a float in combination with the melting pot, the amount of dross which forms in the pots and has to be removed is very greatly reduced. Removal need only be carried out at intervals of seven days or longer. In the usual arrangement without the float, the dross has to be removed several times in twenty-four hours. It is also found that the composition of lead alloys can be kept substantially constant by the use of the float so that the usual allowance of losses for melting need not be made.

A better idea of the advantages to be obtained by the invention is given by the results a trial undertaken with a six ton capacity lead melting pot constructed as described above with reference to the drawings. During this trial, which extended over a period of two weeks, one hundred tons of lead were melted, molten metal being run off at intervals for use in lead presses. Throughout the entire period of two weeks the float was maintained in position. At the end of this period it was removed and the dross and other accumulated foreign matter arising from the surface of the pigs was then skimmed off. On weighing, it was ascertained that 190 (one hundred and ninety) pounds of dross etc. had been produced representing .085% (point nought eight five per cent) of the metal melted. Generally when open type pots are used requiring removal of the dross etc. at more frequent intervals, the amount of dross etc. is of the orderof 1% (one per cent) which is approximately twelve times as much as is produced when the pot is provided with a float in accordance with the present invention.

I claim as my invention:

1. In combination a vessel for containing molten metal and an impermeable body, which is of solid material and structurally stable at the temperature of the molten metal adapted to float on the surface of said metal, the said body comprising a horizontally extending float which follows the shape of the vessel with only sufficient clearance to ensure free movement thereof as the level of the molten metal rises or falls.

2. Apparatus for inhibiting chemical combination between molten metal and the surrounding atmosphere, comprising a vessel for containing molten metal, an impermeable float, of solid material, and structurally stable at the temperature of the molten metal and adapted to float on the surface of the molten metal and cover said surface almost completely, and a continuous downwardly extending flange provided on the lower face of the said float around the edge thereof.

3. Apparatus for inhibiting chemical combination between molten metal and the surrounding atmosphere comprising a vessel for containing the molten metal, an impermeable float, of solid material, and structurally stable at the temperature of the molten metal, adapted to float on the surface of the molten metal and cover said surface almost completely and having a charging aperture therein, means for closing said aperture, and a continuous downwardly extending flange provided on the lower face of the said float around the edge of the aperture therein.

4. Apparatus for inhibiting chemical combination between molten metal and the surrounding atmosphere, comprising a vessel for containing the molten metal, an impermeable horizontally extending body, structurally stable at the temperature of the molten metal and adapted to float on the surface of the said metal, provided with a charging aperture, and at least one trap door for closing the said charging aperture, said door also being adapted to float on the surface of said metal.

5. Apparatus for inhibiting chemical combination between molten metal and the surroundtion between molten metal and the surrounding atmosphere, comprising a vessel for containing the molten metal, an impermeable horizontally extending body, structurally stable at the temperature of the molten metal, adapted to float on the surface of said metal and having a charging aperture therein, and at least one trap door for closing said aperture, said trap door being pivotally connected at one end to the said body and normally maintained in its closing position by the upward thrust of the said molten metal.

HARRY HILL. 

